Load compensating hydraulic circuit

ABSTRACT

A hydraulic circuit for automatically initiating operation of a first, controlled hydraulic ram in response to the pressure build up in a second controlling hydraulic ram including a sequence control valve having an inlet port and a pressure port connected to the controlling hydraulic ram and an outlet port connected to the controlled hydraulic ram. The valve opens in direct response to the build up of pressure in the controlling ram to interconnect the inlet and outlet ports and thereby initiate operation of the controlled ram. A hydraulic valve connected in the drain line of the sequence control valve can be utilized to vary the response of the valve to operate at selected values of pressure built up in the controlling ram and may also be used to lock out the control valve.

[451 Apr. 4, 1972 LOAD COMPENSATING HYDRAULIC CIRCUIT [72] Inventors: Elton B. Long, Burlington; Arthur G.

Short, Bettendorf, both of Iowa [73] Assignee: J. I. Case Company, Racine, Wis.

22 Filed: July 24, 1969 [21] App1.No.: 844,563

[52] US. Cl ..214/138, 214/762 [51] Int. Cl. ..E02i 3/74 [58] Field olSearch ..214/762, 132, 138; 37/103, 37/ 1 17.5

[56] References Cited UNITED STATES PATENTS 2,890,805 6/1959 Pilch ..214/138 2,945,351 7/1960 Westveer ....2l4/l38 X 3,156,098 11/1964 La Rou ....2l4/138X 3,339,763 9/1967 Caywood et a1. ..214/138 3,478,646 11/1969 Cryder et a1. ..214/762 X FOREIGN PATENTS 0R APPLICATIONS 645,458 7/1962' Canada ..37/118 A Primary Examiner-Gerald M. Forlenza Assistant ExaminerFrank E. Werner Attorney-Dressler, Goldsmith, Clement & Gordon [5 7] ABSTRACT A hydraulic circuit for automatically initiating operation of a first, controlled hydraulic ram in response to the pressure build up in a second controlling hydraulic ram including a sequence control valve having an inlet port and a pressure 5 Claims, 2 Drawing Figures BACKGROUND Digging and excavating in improved areas, e.g., digging trenches for foundations, for laying pipe or for similar operation, is usually performed by articulated, powered digging mechanisms adapted to be mounted on agricultural or industrial tractors or similar vehicles. Typical of such articulated digging mechanisms are those commonly identified as backhoes.

Backhoes usually consist of a plurality of articulated members interconnected for relative pivotal movement and connected at one end to the tractor and having a bucket connected to the free end to perform the digging or excavating operations. In a typical backhoe arrangement, a boom is horizontally and vertically pivotably mounted on a support structure located at the rear of a tractor. A hydraulic ram connected between the boom and the support structure is operable to raise and lower the boom.

A dipper arm which is pivotably connected to the free end of the boom carries at its outer, free end the bucket. A hydraulic ram interconnects the boom and the dipper arm and is operable to pivot the dipper arm relative to the boom causing the bucket to move towards the tractor in digging operation. A third hydraulic ram connects the bucket to the dipper arm and is operable to pivot the bucket relative thereto to facilitate raising a loaded bucket and dumping the load from the bucket at a desired location.

Backhoes are often used in areas where the land has been improved, i.e., in which there are already underground installations of water mains, sewage pipes, electrical conduits and the like. It can be appreciated that as the dipper arm is pivoted to draw the bucket through the ground, the bucket may engage an obstruction such as the aforementioned improvements causing severe damage or destruction to such improvements.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a hydraulic circuit in which the operation of one hydraulic ram is automatically initiated in response to the build up of pressure in another hydraulic ram. Such a hydraulic circuit is particularly useful, for example, in connection with the articulated elements of a backhoe whereby engagement of an obstruction by a bucket during the digging operation would cause the boom to be raised allowing the bucket to ride over the obstruction.

Thus, as the bucket at the end of the dipper arm being pivoted in the digging operation engages an obstruction, back pressure builds up in both the bucket hydraulic ram and the dipper arm hydraulic ram. A sequence control valve connected to the pressurized portion of one of these hydraulic rams, i.e., the controlling ram, opens in response to the build up of back pressure to hydraulically interconnect the controlling ram to the controlled ram thereby initiating operation thereof to raise the boom and cause the bucket to clear the obstruction.

The simplicity of the hydraulic circuit of the present invention, in that includes only a direct hydraulic, connection between the two hydraulic rams through the sequence control valve, is particularly advantageous in that the sequence control valve can operate directly in response to the build up of back pressure in the controlling ram to immediately initiate operation of the controlled ram in response thereto. Furthermore, since it is the back pressure in the controlling ram which operates to open the sequence valve, operation of the valve can readily be adjusted by varying the bias force which normally maintains the valve closed thereby selectively adjusting the back pressure required to initiate operation of the control valve.

The simplicity of the valve structure utilized in the hydraulic circuit of the present invention allows the sequence control valve to be selectively locked out when desired. Thus in connection with the use of the circuit with the articulated elements of a backhoe, the sequence control valve might be locked out when obstructions in the path of a bucket are to be overcome rather than avoided.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and of one embodiment thereof, from the claims and from the accompanying drawings in which each and every detail shown is fully and completely disclosed as a part of this specification, in which like numerals refer to like parts.

THE DRAWINGS FIG. 1 is a side view of a typical backhoe arrangement showing the bucket engaging an obstruction; and

FIG. 2 is a schematic view of a hydraulic system including a hydraulic circuit in accordance with the present invention.

DETAILED DESCRIPTION FIG. 1 shows a tractor 10 on the rear end of which is mounted an articulated digging mechanism such as a backhoe 12. The backhoe 12 consists of a boom 14 horizontally and vertically pivotally mounted on a support member 16 attached to the rear of the tractor 10.

A hydraulic ram 18 connected between the boom 14 and support member 16 is operable to raise and lower the boom 14. More particularly, the boom hydraulic ram 18 consists of a hydraulic cylinder 20, one end of which is pivotally connected to the boom at 21, and a piston 22, having a piston rod 24 extending out of the other end of cylinder 20 and pivotally connected to the support member 16 at point 25.

A dipper arm 26 is pivotally connected to the boom 14 at point 27 intermediate the ends of the dipper arm 26. The dipper arm 26 carries at its outer end a bucket 28 pivotally connected thereto at point 29.

A hydraulic ram 30 interconnects the other end of the dipper arm 26 and the boom 14. More specifically, the dipper arm hydraulic ram 30 includes a cylinder 32, one end of which is connected to a bracket 34 on the boom 14, and a piston 36 having a piston rod 38 extending out of the other end of cylinder 32 and connected to point 39 on the dipper arm 26.

The bucket 28 is pivoted relative to the end of the dipper arm by another hydraulic ram 40 consisting of a cylinder 42, connected at one end to the dipper arm 26 at point 43, and a piston 45 having a piston rod 46 extending out of the other end of the cylinder 42 and connected to the bucket 28 at point 47.-

In the digging operation, the boom 14 is lowered and the dipper arm 26 is pivoted in a clockwise direction, as seen in FIG. 1, towards the tractor 10. If, during this operation, the bucket 28 engages an obstruction, such as pipe 48, it is often desirable to be able to raise the bucket 28 to clear the obstruction 48 to allow the digging operation to continue without damage to the obstruction 48.

A hydraulic circuit 50 for effecting the desired compensation is part of the hydraulic system shown in FIG. 2.

The hydraulic system shown schematically in FIG. 2 is a standard hydraulic system in which hydraulic power is applied to the various hydraulic rams 18, 30, 40, under control of the master control valve 52. Thus, the boom 14 is raised by applying hydraulic power through hydraulic line 54 to the rod end of the boom cylinder 20 and lower by applying hydraulic power to the piston end of cylinder 20 through hydraulic line 56.

The dipper arm is pivoted in a clockwise direction (as seen in FIG. 1) for digging by applying hydraulic power to the piston end of hydraulic cylinder 32 through hydraulic line 58, and pivoted in the opposite direction by applying hydraulic power to the rod end of the cylinder 32 through hydraulic line 59. Similarly, the bucket 28 is pivoted rearwardly relative to the dipper arm 26 by applying hydraulic power to the piston end of the bucket cylinder 42 through hydraulic line 60 and pivoted in the opposite direction by applying hydraulic power to the rod end of the bucket cylinder 42 through hydraulic line 61.

During the digging operation, the boom 14 is usually lowered to a set position and the dipper arm 26 pivoted in a clockwise direction (as seen in FIG. 1) towards the tractor by applying hydraulic power through hydraulic line 58 to the piston end of the dipper arm cylinder 32. It can be-appreciated that when the bucket 28 at the end of the dipper arm 26 engages an obstruction 48, the increased resistance to the pivoting movement of the dipper arm 26 is reflected in an increase in back pressure at the piston end of the dipper cylinder 32 and at the piston end of the bucket cylinder 42.

This back pressure in either the dipper cylinder 32 or the bucket cylinder 42 can be utilized to raise the boom 14 and thereby the bucket 28, to allow the bucket to ride over and thereby bypass the obstruction 48.

This compensation is effected by connecting the piston end of the dipper arm cylinder 32, or the bucket cylinder 42 to the rod end of the boom cylinder through a normally closed sequence control valve 62. While, as indicated above, either the dipper arm cylinder 32 or the bucket cylinder 42 can be connected to the boom cylinder 20, only the dipper arm cylinder is shown in FIG. 2 so connected for convenience and clarity.

The sequence control valve 62 includes a valve body 64 having a generally axial bore 66. A pressure port 68 is formed at one end of the bore 66 while intermediate the end of the bore there are an inlet port 70 and an outlet port 72 in the form of circumferential recesses surrounding the bore 66. The drain port 74 is formed at the opposite end of the bore 66 from the pressure port 68. The pressure port 68 and inlet port 70 are connected to the piston end of dipper cylinder 32 through hydraulic lines 58 and 75, while outlet port 72 is connected to the rod end of the boom cylinder 20 through hydraulic lines 54 and 76.

A valve spool 77 having two land portions 78, 80 spaced apart by a narrow neck portion 82 is slidably mounted in the bore 66 and biased toward the pressure port 68 by a suitable biasing means such as spring 84. When the valve spool 77 is in its normal or closed position, land portion 78 separates the pressure port 68 from the inlet port 70, while land portion 80 separates the inlet port 70 from the outlet port 72.

A back pressure present in the piston end of the dipper cylinder 32 is transmitted through lines 58 and 75 to the pressure port 68. When this back pressure reaches a selected level sufficient to overcome the resistance of the bias force, e.g., spring 84, the valve spool 77 slides within the bore 66 away from the pressure port to open the valve, In the open position, the neck portion 82 of the spool 77 interconnects the inlet port 70 and the outlet port 72 The hydraulic pressure is thus transmitted from the dipper cylinder 32 directed to the rod end of the boom cylinder 42 through the now open sequence control valve 62 to initiate operation of the boom ram 18 causing the boom 14 to be raised. The piston end of the boom cylinder 20 is connected to the reservoir 86 through a relief valve 88 to complete the hydraulic circuit.

There are occasions, particularly when the apparatus is being utilized in unimproved or rocky terrain where it is not desirable to raise the boom 14 as the bucket 28 engages various obstructions. A lock out valve 90, provided in the drain line 92 connected to the drain port 74 of the sequence control valve 62 can be closed to lock out the sequence control valve thereby preventing transmission of the back pressure generated in the dipper cylinder 32 to the boom cylinder 20. Such a lock out valve 90 may also be utilized to hydraulically adjust the bias force on the valve spool 77 thereby selectively adjusting the level of the back pressure required to initiate operation of the hydraulic compensating circuit.

Although either the dipper ram 30 or the bucket ram 40 can be utilized to initiate operation of the boom ram 18, one advantage of utilizing the dipper ram 30 is that opening of the sequence control valve 62 limits hydraulic power to the dipper ram 30 thereby interrupting the digging operation of the dipper arm 26 while the boom 14 is being raised to avoid obstructions.

Thus, there has been disclosed a hydraulic compensating circuit in which operation of a first controlled hydraulic ram is initiated in response to the build up of a selected pressure in a second controlling hydraulic ram selectively connected thereto by a sequence control valve the operation of which is initiated in direct response to the build up of a selected pressure level in the controlling ram. The sequence valve involves relatively few moving parts and includes means for locking out the valve when operation of the first ram is not desired.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

What is claimed is:

l. A load compensating hydraulic circuit for a backhoe having a vertically pivotal boom, a dipper stick supported on said boom for vertical pivotal movement with respect thereto, and

a bucket pivotally supported at the free end of said dipper stick; said hydraulic circuit comprising first hydraulic ram means connected to said boom and operable to raise and lower said boom, second hydraulic ram means interconnecting said boom and said dipper stick and operable to pivot said dipper stick vertically relative to said boom, a sequence control valve, first hydraulic conduit means providing a direct hydraulic connection between said first ram means and said sequence control valve, second hydraulic conduit means providing a direct hydraulic connection between said second hydraulic ram means and said sequence control valve, pressure conduit means providing a second direct hydraulic connection between said second hydraulic ram means and said sequence control valve, means biasing said sequence control valve closed, said sequence control valve opening in direct response to an increase in pressure in said pressure conduit means reflecting an increase in pressure in said hydraulic ram means to a selected level sufficient to overcome said biasing means and hydraulically interconnecting said first and second hydraulic conduit means, whereby operation of said first hydraulic ram means is initiated in direct response to said increase in pressure in said second hydraulic ram means.

2. A load compensating hydraulic circuit as claimed in claim 1 wherein said sequence control valve includes an inlet port, an outlet port and a pressure port, means connecting said first conduit means to said outlet port, means connecting said second conduit means to said inlet port, and means connecting said pressure conduit means to said pressure port, said valve opening in response to said increase in pressure at said pressure port to hydraulically interconnect said first and second hydraulic rams through said inlet and outlet ports.

3. A load compensating hydraulic circuit as claimed in claim 2 including a drain port in said sequence control valve, and lock out means hydraulically connected to said drain port and selectively operable to close said drain port and prevent operation of said sequence control valve.

4. A load compensating hydraulic circuit as claimed in claim 1 including means for hydraulically varying the biasing force to vary the value of the selected pressure at which said valve opens.

5. An earth moving apparatus comprising a boom member, means for supporting one end of said boom member for vertical pivotal movement, a bucket, means for pivotally supporting said bucket on the other end of said boom member, first hydraulic ram means connected between said boom support means and said boom member and operable to raise and lower said boom member in response to hydraulic pressure, second hydraulic ram means connected between said boom member and said bucket support means and operable to pivot said bucket relative to said boom member in response to hydraulic ing means to hydraulically interconnect said first and second hydraulic ram means and thereby apply hydraulic pressure to said first hydraulic ram means to raise said boom, and lock out valve means hydraulically connected to said sequence control valve and selectively operable to lock said sequence control valve to prevent its opening in response to said selected increase in back pressure. 

1. A load compensating hydraulic circuit for a backhoe having a vertically pivotal boom, a dipper stick supported on said boom for vertical pivotal movement with respect thereto, and a bucket pivotally supported at the free end of said dipper stick; said hydraulic circuit comprising first hydraulic ram means connected to said boom and operable to raise and lower said boom, second hydraulic ram means interconnecting said boom and said dipper stick and operable to pivot said dipper stick vertically relative to said boom, a sequence control valve, first hydraulic conduit means providing a direct hydraulic connection between said first ram means and said sequence control valve, second hydraulic conduit means providing a direct hydraulic connection between said second hydraulic ram means and said sequence control valve, pressure conduit means providing a second direct hydraulic connection between said second hydraulic ram means and said sequence control valve, means biasing said sequence control valve closed, said sequence control valve opening in direct response to an increase in pressure in said pressure conduit means reflecting an increase in pressure in said hydraulic ram means to a selected level sufficient to overcome said biasing means and hydraulically interconnecting said first and second hydraulic conduit means, whereby operation of said first hydraulic ram means is initiated in direct response to said increase in pressure in said second hydraulic ram means.
 2. A load compensating hydraulic circuit as claimed in claim 1 wherein said sequence control valve includes an inlet port, an outlet port and a pressure Port, means connecting said first conduit means to said outlet port, means connecting said second conduit means to said inlet port, and means connecting said pressure conduit means to said pressure port, said valve opening in response to said increase in pressure at said pressure port to hydraulically interconnect said first and second hydraulic rams through said inlet and outlet ports.
 3. A load compensating hydraulic circuit as claimed in claim 2 including a drain port in said sequence control valve, and lock out means hydraulically connected to said drain port and selectively operable to close said drain port and prevent operation of said sequence control valve.
 4. A load compensating hydraulic circuit as claimed in claim 1 including means for hydraulically varying the biasing force to vary the value of the selected pressure at which said valve opens.
 5. An earth moving apparatus comprising a boom member, means for supporting one end of said boom member for vertical pivotal movement, a bucket, means for pivotally supporting said bucket on the other end of said boom member, first hydraulic ram means connected between said boom support means and said boom member and operable to raise and lower said boom member in response to hydraulic pressure, second hydraulic ram means connected between said boom member and said bucket support means and operable to pivot said bucket relative to said boom member in response to hydraulic pressure, said second hydraulic ram means generating increased back pressure in response to said bucket engaging an obstruction during pivoting thereof, a sequence control valve, means normally biasing said sequence control valve closed, hydraulic conduit means connecting said pressurized second hydraulic ram means to said valve and said valve to said first hydraulic ram means, said valve opening in response to a selected increase in said back pressure in said pressurized second hydraulic ram means sufficient to overcome said biasing means to hydraulically interconnect said first and second hydraulic ram means and thereby apply hydraulic pressure to said first hydraulic ram means to raise said boom, and lock out valve means hydraulically connected to said sequence control valve and selectively operable to lock said sequence control valve to prevent its opening in response to said selected increase in back pressure. 